Method for coating steel

ABSTRACT

WHERE R&#39;&#39; is hydrogen, methyl or ethyl and R is methyl, ethyl, or hydroxymethyl, heating to effect further polymerization, applying thereto a solution or a dispersion of a vinyl halide polymer, copolymer, or terpolymer and heating to effect evaporation of the solvent or coalescence of the dispersion.   A process for coating steel by applying thereto a monomer or partial polymer of an amide, represented by the formula

United States Patent [191 Sausaman et al.

[451 Jan. 15, 1974 METHOD FOR COATING STEEL [22] Filed: Jan. 14, 1972[21] Appl. No.: 218,013

[52] US. Cl. ..117/75,117/132 B, 117/161 UA [51] Int. Cl B32b 15/08,B44d 1/36 [58] Field of Search 117/75, 161 UA, 132 B, 117/132 C;260/89.? R

[56] References Cited 1 UNlTED STATES PATENTS 3,050,412 8/1962 Coe117/75 3,700,635 10/1972 Brust et a1... 260/89.7 R

3,418,157 12/1968 Katzer 117/161UA Primary Examiner-Murray KatzAssistant Examiner-Harry J. Gwinnell Attorney-Robert H. Dewey and HowardE. Post [5 7] ABSTRACT A process for coating steel by applying thereto amonomer or partial polymer of an amide, represented by the formula whereR is hydrogen, methyl or ethyl and R is methyl, ethyl, or hydroxymethyl,heating to effect further polymerization, applying thereto a solution ora dispersion of a vinyl halide polymer, copolymer, or terpolymer andheating to effect evaporation of the solvent or coalescence of thedispersion.

9 Claims, No Drawings METHOD FOR COATING STEEL BACKGROUND OF THEINVENTION This invention relates to an improved method for coatingsteel. In a particular aspect this invention relates to a method forcoating steel with a vinyl chloride polymer, copolymer or terpolymer andheating to effect the finished coating.

It is known to employ polymers and copolymers of vinyl chloride as aprotective coating on steel and the steel so coated has many desirableproperties. However, the use of such coatings has been disadvantageousbecause vinyl chloride polymers and copolymers are sensitive to thepresence of ions of iron and undergo degradation when heated. Therefore,vinyl chloridebased solutions and dispersions applied to ferrous metalscannot be heated at elevated temperatures. Drying of solutions byevaporation at ambient temperatures requires a substantially longerdrying time. Hence the output from the assembly line of vinyl coatedarticles is greatly reduced as compared with coated articles which canbe force dried. Accordingly, there has been a need for an improvedmethod for coating steel with vinyl chloride polymers, copolymers andterpolymers so that coatings based on these polymers can be bakedwithout risk of degradation.

SUMMARY OF THE INVENTION It is an object of this invention to provide animproved method for coating steel.

It is another object of this invention to provide a method forprotecting from degradation due to iron ions vinyl chloride polymers andcopolymers applied to steel.

It is yet another object of this invention to provide a method ofcoating steel with vinyl chloride polymers and copolymers whereby thecoating can be baked.

Other objects will be apparent to those skilled in the art from thedisclosure herein.

An improved method for coating the surface of a ferrous object with avinyl chloride polymer or copolymer has been discovered. According tothe present invention the ferrous surface to be coated is first coatedwith a film consisting essentially of a monomer or preferably a partialpolymer, including partial copolymers, of a bisor tris-(hydroxymethyl)acrylamide, or a solution thereof, corresponding to the formula where Ris hydrogen, methyl or ethyl, and R is methyl, ethyl or hydroxymethyl. Asolution or a dispersion of particles of the vinyl chloride polymer orcopolymer is then applied to the amide film and baked at a temperatureof about 250-450F, thereby evaporating the solvent from the solution, orcoalescing the particles of the dispersion.

DETAILED DISCUSSION The acrylamides suitable for the practice of thisinvention include but are not limited to acrylic, methacrylic orethylacrylic amides of alkanolamines corresponding to the formula whereR has the same meaning described hereinbefore.

These amides can be prepared by reacting an alkanolamine correspondingto the above formula with a lower alkyl ester of an acid correspondingto the for mula where R has the same meaning described hereinbefore. Theterm lower alkyl ester includes generally esters of alcohols of one tofour carbon atoms.

This reaction is effected in the presence of a catalyst and apolymerization inhibitor at reflux temperatures thereby forming saidamide. The amide is then filtered to remove any solids, e.g., catalyst,and is then generally suitable for the practice of this invention.

More particularly, the amides useful in the present invention areprepared as follows. The alkanolamine and the acrylate ester are mixedin a mole ratio of from about 0.8-1.2 moles of alkanolamine per mole ofester. Preferably, however, the ratio is within the range of 0.9-1.1:1,respectively, and a ratio of about 0.9:1 is particularly preferred. Tothe mixture is added a catalyst in an amount of about 0.0250.25 g/lOO gof reactants, and a polymerization inhibitor in an amount of about0.05O.l g/ 100 g of reactants. The reaction mixture is then transferredto a reaction vessel equipped with a reflux condenser, a heat source, apressure reduction means, and a take-off head.

The mixture is heated, generally but not necessarily at reducedpressure, under total reflux conditions until it is determined that thealkanol portion of the ester is being separated. The'reflux ratio isthen preferably, but not necessarily, adjusted initially to about 3:1and then eventually to total take-off, whereby the alkanol, as well asany excess acrylic or methacrylic ester, is separated from the reactionmixture.

The reaction mixture in the vessel is an alkanolamide corresponding tothe formula where R and R have the same meaning hereinbefore defined.

The alkanolamide is then decanted or preferably, but not necessarily,filtered to remove any insoluble material.

The alkanolamines suitable for preparing the amides useful for thepractice of this invention are those in which, to the carbon atomadjacent to the amino group, there are bonded three hydroxylakyl groupsor two hydroxyalkyl groups and an alkyl group, e.g. methyl or ethyl.These alkanolamines include but are not limited to2-amino-2-methyl-l,3-propane-diol; 2-amino-2- ethyl-1,3-propanediol; and2-amino-2-hydroxy-methyl- 1,3-propanediol. These latter compounds arepreferred because they are commercially available and the usualcommercial grade is suitable for the practice of this invention. Otheralkanolamines meeting the foregoing definition are also suitable.

Suitable esters include, but are not limited to, the methyl and ethylesters of acrylic and methacrylic acid. These esters are commerciallyavailable and the usual commercial grades are suitable for the practiceof this invention. The methyl ester is preferred, e.g. for reasons ofeconomy.

Suitable catalysts include lithium metal, or alkoxides of lithium,sodium or potassium. The alkoxides can be the methoxides, ethoxides,propoxides or butoxides, preferably the methoxide. The particularlypreferred catalyst is lithium metal, preferably in sub-divided form. Theamount of catalyst used is generally in the range of about 0.025 to 0.25g/l g of reactants. Generally about 0.025g/ 100 g is sufficient andtherefore preferred.

The polmerization inhibitor can be any of the inhibitors known in theart, of which there are many, or a mixture thereof. Typical inhibitorsinclude, but are not limited to, substituted catechols, 2,6-di-tertiarybutyl- 4-methylphenol (e.g. lonol, marketed by Shell Chemical Company),and substituted hydroquinones such as 2,5-di-tertiary-amyl hydroquinoneand 2,5-di-tertiary butyl hydroquinone.

The preferred acrylamide for the practice of this invention is N-[ l,1-bis(hydroxymethyl)ethyl]- l methacrylamide. Others suitable for thepractice of this invention include but are not limited to:

N- tris( hydroxymethyl )methyl l -methacrylamide N-[ 1, l-bis(hydroxymethyl)propyl]- l methacrylamide N-[ l, l-bis(hydroxymethyl)ethyl]- 1 -acrylamide N-[ l,1-bis(hydroxymethyl)ethyl]-1-ethacrylamideN-[1,1-bis(hydroxymethyl)propyl]-l-ethacrylamide N-[tris( hydroxymethyl)methyl]- 1 -ethacrylamide N-[ l l -bis( hydroxymethyl)propyl]- 1-acrylamide Partial polymers of the foregoing acrylamides are preferredfor the practice of this invention. The term partial polymer as usedherein is intended to mean a polymer of somewhat higher molecular weightthan the starting monomer, but capable of further polymerization atelevated temperatures or in the presence of a polymerization catalyst,many of which are know. These acrylamides can be partially polymerizedin several ways. One method is to permit them to age at ambienttemperatures for several weeks. Another method is to expose them toultraviolet radiation for several hours, e.g. 5-15 hours. Yet anothermethod is to heat the monomer at about 80C in the presence of acatalyst, about 1 percent, for about 30 minutes. Suitable catalystsinclude di-tertiary butyl peroxide, tertiary butyl peroxypivalate, anddicumyl peroxide.

The acrylamide or partial polymer thereof is applied to the steelsurface by any covenient method, i.e. by wiping, roller, brush, spray,calendaring, etc., in a quantity sufficient to provide a baked film ofpreferably about 0.05l mil. These amides and partial polymers thereofare liquids and can be applied to the steel undiluted. When desired,however, they are diluted to about l-80 percent with any suitablesolvent, many of which are known in the art. Typical solvents which canbe used include, but are not limited to, lower alkanols, esters,ketones, aliphatic and aromatic hydrocarbons, nitroalkanes andchlorinated hydrocarbons. Preferred solvents include dimethyl formamide,Z-nitropropane, toluene and xylene. It is not intended that theinvention be limited as to the method of applying the acrylamide orpartial polymer thereof, nor limited as to the nature of the solvent,nor limited as to the concentration of amide in the solvent.

The steel article coated with the amide is heated to about 250-450F fora period of time sufficient to cause it to further polymerize. Theheating, or baking step, is well known in the art of coating steel andany of the known methods are suitable for the practice of thisinvention. For example, the heating step can be effected by passing thearticle into a heated oven, or passing the steel over a flame or anelectrically-heated element, etc. A heating period of 5-30 seconds ormore is generally sufficient.

The steel article is then permitted to cool, e.g. to below about 60C,preferably about 30. A solution or dispersion (i.e. an organosol orplastisol") of vinyl chloride polymer or copolymer is then applied byany suitable method, some of which were set forth above, in an amountsufficient to provide a dried film of about 1-2 mils or more as desired.The steel article is then again heated to 250-450F for a period of timesufficient to evaporate the solvent, when the polymer is applied as asolution, or to coalesce the film when applied as a dispersion, i.e.generally 0.5 to 5 minutes.

The term steel article and ferrous surface" are intended to meanarticles of steel, iron and alloys thereof, including but not limited tocarbon steel, stainless steel, monel metal, wrought iron, cast iron, andthe like, having a significant iron content, i.e. sufficient to causedegradation of vinyl halide polymers at elevated temperatures.

Suitable vinyl chloride polymers and copolymers include but are notlimited to those generally designated coating" resins. Generally theyconsist of vinyl chloride, copolymers of vinyl chloride -98 percent,vinyl acetate 2-25 percent and maleic acid, 0-2 percent.

Other coating resins include terpolymers of vinyl chloride 88-92 percentwith acetate 3-5 percent and vinyl alcohol 5-7 percent; vinyl chloride75-85 percent with vinyl acetate 14-20 percent, and glycidylmethacrylate 1-5 percent; vinyl chloride 40-80 percent and vinylidenechloride 20-60 percent; vinyl chloride and monoor dibutyl acid maleates,or mixtures thereof having inherent viscosities of from about 0.2 to1.8. It is not intended that the practice of this invention be limitedto any particular vinyl chloride polymer or copolymer because theinvention. can advantageously be used with any such polymer whichdeteriorates in the presence of ions of iron.

Solvents for the above vinyl copolymers are well known in the art. Theyinclude ketones, i.e. methyl ethyl ketone, methyl isobutyl ketone,cyclohexanone, tetrahydrofuran, mixtures of aromatic hydrocarbons andnitroalkanes, esters, chlorinated hydrocarbons, etc. The formulation anduse of such solutions are wellknown in the art and it is not intendedthat the practice of this invention be limited to any particular vinylchloride polymer or eopolymer or solution thereof.

The practice of this invention is not limited to solutions of vinylchloride polymers and copolyers but is equally applicable todispersions. Generally, these dispersions consist of comminuted highmolecular weight vinyl chloride polymers dispersed in a volatile medium,e.g. an aliphatic hydrocarbon, (a composition commonly designatedorganosols"), or a non-volatile plasticizer, e.g. dioctyl phthalate, (acomposition commonly designated a plastisol"). Upon heating, theparticles coalesce, and, in the case of organosols, the mediumevaporates.

The invention will be better understood with reference to the followingexamples. It is understood, however, that the examples are intended forillustration only, and it is not intended that the invention be limitedthereby.

EXAMPLE 1 2-Amino-2-ethyl-l,3-propanediol (AEPD), 119 g (1 mole) andmethyl methacrylate, 100 g (1 mole) were charged to a 500 mlround-bottom flask equipped with an agitator, an air sparger, and athermometer. Sodium methoxide 0.50 g and ditertiary-amyl hydroquinone(AHQ), 0.50 g, dispersed therein. Dry air was introduced under thesurface of the liquid and heat was applied to the reaction mixture atatmospheric pressure. The column head was set for total reflux. At avapor temperature of 65 and a liquid temperature of 95, distillateremoval was begun at a reflux ratio 3:1. After about two hours, theliquid temperature had risen to 136 and the vapor temperature to 67.About 28 g of distillate mostly methanol had been collected. Thereaction product in the pot was N-[1,1- bis(hydroxymethyl )-ethyl] l-methacrylamide.

A film of 0.1 mil thickness of the foregoing amide was applied by wipingto one half of a steel D-panel. It was polymerized by baking for 1minute at 400F.

A solution of a copolymer of vinyl chloride and butyl maleate wasapplied over the entire panel in a quantity sufficient to form a dryfilm, after evaporation of solvent, of 0.6 i 0.2 mil thickness. Thevinyl chloride was in a ratio of 3:1 to the butyl maleate, whichconsisted of dibutyl maleate and mono-butyl maleate in a ratio of 4:1(Exon 470 manufactured by Firestone Tire and Rubber Company was thecopolymer used). It was dissolved in a mixture of toluene and methylisobutyl ketone in about a 1:1 ratio thereby forming a solutioncontaining 20 percent by weight of solids.

The coated panel was baked for min. at 400F. The vinyl copolymer ctingover the amide was intact, though moderately discolored, whereas thevinyl copolymer applied to bare steel was totally degraded, black incolor and lacked film integrity.

EXAMPLE 2 The experiment of Example 1 was repeated in all essentialdetails except that N- [tris(hydroxymethyl)methy]1-1-methacrylamide wasused as the amide. The vinyl chloridemaleate copolymer was protected bythe amide during the baking step.

EXAMPLE 3 The experiment of Example 1 was repeated in all essentialdetails except that the amide film applied to the steel panel waspolymerized by passing the pan through the flame of a Fisher hightemperature gas burner for about two seconds. The coated side of thepanel was maleate film was totally degraded, black in color and lackedfilm integrity.

EXAMPLE 4 The experiment of Example 3 is repeated in all essentialdetails except that N-[ 1,1-

bis(hydroxymethyl)propyl]- l -methyacrylamide is used as the amide. Theamide polymer protects the polyvinyl chloride-maleate film fromdegradation.

EXAMPLE 5 A thin film of N-[l,1-bis(hydroxymethyl)ethyl]-lmethacrylamide was applied to one half ofa steel panel by wiping. The panel was exposed to ultra-violet radiationat a distance of 12 inches from three 40 watt U-V tubes having a peakoutput at 3654A for seven hours, thereby polymerizing the amide.

A 20 percent by wt solution in a 1:1 mixture of methylisobutyl ketoneand toluene of a vinyl chloride/vinyl acetate/maleic acid terpolymerhving a ratio of 84:15zl (the resin used was Bakelite vinyl resin VMCCmanufactured by Union Carbide Corporation, New York) was applied to thepanel in an amount sufficient to provide a dry film of about 0.6 milafter evaporation. The coated panel was baked for 7 min. at 350F. Thevinyl terpolymer protected by the amide polymer was intact and onlyslightly discolored. The unprotected polymer was totally degraded, blackin color, and lacked film integrity.

EXAMPLE 6 A sample of the amide prepared by the procedure of Example 1was partially polymerized by permitting it to age at ambient temperaturefor about two weeks. It was of low molecular weight and had a soft,tacky, rubbery consistency. It was dissolved in a 3:1 mixture of 2-nitropropane and methanol at a concentration of 15 percent. An amountsufficient to provide a dry (by evaporation) film thickness of 0.l milwas drawn down on one-half of a steel panel. The panel was then bakedfor five min. at 350F and allowed to cool.

The vinyl terpolymer solution of Example 5 was applied in an amountsufficient to provide a dry film thickness (by evaporation) of about 0.6mil over the entire panel. It was then baked for seven minutes at 3501F.

The unprotected vinyl film was severely degraded, black, and withoutfilm integrity. The protected vinyl film was unaffected and whollyintact.

EXAMPLE 7 The experiment of Example 6 is repeated in all essentialdetails except that N-[l,1-bis(hydroxymethyl)- ethyl]-l-acrylamide isused as the amide.

The unprotected vinyl film is severely degraded, black, and without filmintegrity. The protected vinyl film is unaffected by heating, but theunprotected film is black and lacking in film integrity.

EXAMPLES 9-ll The experiment of Example 1 is repeated in all essentialdetails except that the vinyl oxazoline identified below is substitutedfor the vinyl oxazoline of Example 1.

Example No. Vinyl Oxazoline 9 N-[ l ,l -bis(hydroxymethyhpropyl1-l-ethacrylamide IO N-[ tris(hydroxymethyUmethyl 1-] -ethacrylamide N-ll,l -bis(hydroxymethyl )propylll -acrylamide We claim:

I. In a process for coating a ferrous surface by first coating with afilm, heating to 250-450F for a period of time sufficient to polymerizesaid film, cooling to about 3060C, aplying thereto a solution in avolatile solvent of a vinyl chloride polymer or copolymer, or adispersion of a comminuted vinyl chloride polymer in a volatile liquidor a non-volatile plasticizer and heating to 250-450F for a period oftime sufficient to effect evaporation of said solvent, or coalescence ofsaid comminuted polymer, the improvement consisting of using as saidfilm an alkanolamide or partial polymer thereof represented by theformula wherein R is hydrogen, methyl or ethyl and R is methyl, ethyl orhydroxymethyl.

2. The process of claim I wherein R of said amide is hydroxymethyl and Ris methyl.

3. The process of claim 1 wherein R of said amide is methyl or ethyl.

4. The process of claim 3 wherein R is methyl or ethyl.

5. The process of claim 3 wherein R is hydrogen.

6. The process of claim 1 wherein R of said amide is hydroxymethyl andR' is ethyl.

7. The process of claim 1 wherein R of said amide is hydroxymethyl and Ris hydrogen.

8. The process of claim 1 wherein said film is said alkanolamide.

9. The process of claim 1 wherein said film is said partial polymer ofsaid alkanolamide.

1mg H UNITED smtrs PATENT QFHCE CERTIHQATE @F CQRREC'HUN Patent3.785.855 Dated January 15, 1974 Inv nt fl n. K- Sauseman and R F,Purcell It is certified that error appears in the above-identifiedpatent and that said Letters Patent are hereby corrected as shown below:

Page 1, after the names addresses of the inventors, insert --[73}Assignees Commercial Solvents Corporation, Terre Haute, Indiana-- Column2, line 59, Y'hydroxylaklyl" should read --hydroxyalkyl Column 4, line38, after with" insert -vinyl-- Column 4, line 61, co oolqgezrs" shouldread -copolymers- Colunm 5, line 15, after "0.G50 9' insert -"-were--Column 5, line 41, "cting" should read -coating- Column 5, line 57,"pan" should read --panel- Column 6, line 7, "methyeorylamide" shouldread -methacrylamide-r 1 Column 6, line 2l, "Ewing" should read--having- Column 7, line 15, claim 1, "aplying'" should read -a.pplyingSigned and sealed this let day of October 1974,

(SEAL) Attest:

MCCOY M, GIBSON JRO c0 VLARSHALL DANN Attesring Officer Commissioner ofPatents L I v s I I J

2. The process of claim 1 wherein R of said amide is hydroxymethyl andR'' is methyl.
 3. The process of claim 1 wherein R of said amide ismethyl or ethyl.
 4. The process of claim 3 wherein R'' is methyl orethyl.
 5. The process of claim 3 wherein R'' is hydrogen.
 6. The processof claim 1 wherein R of said amide is hydroxymethyl and R'' is ethyl. 7.The process of claim 1 wherein R of said amide is hydroxymethyl and R''is hydrogen.
 8. The process of claim 1 wherein said film is saidalkanolamide.
 9. The process of claim 1 wherein said film is saidpartial polymer of said alkanolamide.